The existing oil refineries mostly use the conventional "screw compressor" or "lithium bromide" cooling methods to effect the heat exchange for recovering petroleum gas. However, in those methods:
1. The screw compressor cooling method expends lots of energy, and the exhausting of electric power can not be compensated in cost by the recovered petroleum gas. Therefore refineries scarcely adapt this method except in the case when a prime factor is to protect the environment.
2. The lithium bromide cooling method of petroleum gas recovery also requires the exhausting of cooling media and absorbent (lithium bromide), yet it produces a relatively large volume of discharged heat. As such, it can be a heat contamination source notwithstanding the usage as a heat source of the wasted heat vapor.
Accordingly, most of the refineries in these days still take the torch tower burning method to burn the ethane, propane, butane, and other wasted petroleum gases which are hard to recover with the vapor fractionating tower. This method generates air pollution.